If found guilty, the companies could face unlimited fines. In October 2005, the Crown Prosecution Service said no charges for manslaughter through gross negligence could be brought, a decision that the CPS told the rail regulators last month there were no grounds to review.

The rail regulators' safety director, Ian Prosser, said today: "I have decided there is enough evidence, and it is in the public interest, to prosecute Network Rail and Jarvis Rail for serious health and safety breaches."

More than 70 people were injured when the 12.45 King's Cross to King's Lynn train came off the rails as it approached Potters Bar, where it was not due to stop, at about 1pm on 10 May 2002.

The inquest was held this summer, eight years after the crash – a delay that the coroner, Judge Michael Findlay Baker QC, branded "indefensible".

At the time of the crash, rail infrastructure was the responsibility of Railtrack, whose responsibilities were taken over by Network Rail in October 2002.

Jarvis Rail, the maintenance contractor for the area at the time, went into administration in March 2010.

The companies each face a charge under the 1974 Health and Safety at Work Act for allegedly failing to "provide and implement suitable and sufficient training, standards, procedures and guidance for the installation, maintenance and inspection of adjustable stretcher bars [on points]".

Prosser said: "For the sake of the families involved, we will do all we can to ensure the prosecutions proceed as quickly as possible.

"The railway today is as safe as it has ever been, but there can be no room for complacency. When failings are found, those at fault must be held to account and the entire rail industry must continue to strive for improvements to ensure public safety is never put at similar risk again."

Perdita Kark, the daughter of Austin Kark, who was killed in the crash, said: "It is quite right and proper. The only thing that bothers me is why it has taken nearly nine years to get to this point.

"My feeling is that it should have happened far sooner following the crash. We shouldn't have to have fought so hard and fought so long to get an inquest."

A Network Rail statement said: "The railway today is almost unrecognisable since the days of Railtrack and the Potters Bar tragedy of 2002.

"Private contractors are no longer in control of the day-to-day maintenance of the nation's rail infrastructure since Network Rail took this entire operation, involving some 15,000 people, in-house … All of the recommendations made by both the industry's own formal inquiry and the health and safety investigation have been carried out.

"Today the railways are safer than they have ever been, but our task remains to build on that record and always to learn any lessons we can to make it ever safer for passengers and those who work on the railway."

Bob Crow, the general secretary of the Rail Maritime and Transport union, said the decision to prosecute was "better late than never".

"We will also be watching closely for any attempts by the directors of Jarvis Rail to avoid being called to account for their actions following the collapse of the company," he added.

"This prosecution also sends out a clear warning to those currently responsible for rail maintenance, and the government in this climate of cuts to transport budgets, that anyone caught playing fast and loose with rail safety can expect to feel the full force of the law."

Gerry Doherty, the leader of the TSSA rail union, said: "At long last we are going to find just who was responsible for this tragedy."

The case is expected to open at Watford magistrates court in Hertfordshire on 11 January next year.